Rock-over method for establishing gas-lift operations in oil wells



.177,1929. Ew. LAKE 1,740,105

ROOK OVER METHOD FOR ESTABLISHING GAS LIFT OPERATIONS `IN OIL WELLSFiled July 18, 1927 N www @E BY A T'TORNE y Patented Dec. l?, 1929PATENT OFFICE FRANCIS W. LAKE, `OIE' WHITI'IER, CALIFORNIA, ASSIGNOR TOUNION OIL COMPANY OF CALIFORNIA, OF LOS ANGELES, CALIFORNIA, ACORPORATION OF CALIFORNIA ROCK-OVER METHOD FOR ESTABLISHING GAS-LIFTOPERATIONS IN OIL WELLSA Application led July 18, 1927. Serial No.`2(),6,681.

This invention relates to the so-called gas lift method of flowing deepwells, particularly oil wells, and has been designed to overcome theexcess hydrostatic head of oil which 5 ordinarly accumulates in suchwells prior t0 starting gas lift and which ordinarily cannot be removedby direct application of a reasonable gas pressure in attempting to1ni'tiate gas lift.

D Gas lift, as now/.commonly practiced, consists in passing gasunderpresure into a well containing a flow tube, soithat the gas passesaround the lower end of the flow'tube in a stream and in itspassageatmniZes-the oil as fast as it is forced up to said tube end bythe natural rock pressure in the well, the atomized oil being carried tothe surface in the gas stream. The gas may be introduced either throughthe iow tube or through the casing, the atomized oil being dischargedfrom the other of the two; however, it is preferred usually to introducethe gas into the casing and discharge the oil fro`m the iiow tube. 52"But, as above indicated, the initiation of gas liftusuallyoifers'diiiculties, due to the fact that during a preceding period ofidleness a relatively great hydrostatic head of 'oil has accumulated inthe well hole, which 3U head usually cannot be overcome by steadyapplication of a moderate pressure to one side 'of the flow tube. This-condition arises for the reason that, as pressure is applied to oneside of the tube to depress the oil level therein, the hydrostatic 'headincreases in the other side. lVhile some of the oil is forced back intothe formation (de ending upon the viscosity of the oil, the riction ofthe Cab formation, and the like) the eifectiverock pressure in thevicinity of the well increases until it is suicient to balance theincreased hydrostatic head. Thus, upon any attempt to start gas lift bystraight lapplication of pressure to one side in order to force over theentire excess load of accumulated oil and uncover the lower end of thetube for passage i of gas thereunder, the hydrostatic head will increaseuntil it reaches the maximum, that is, until it is equal to theentire'height of the flow tube, which height may be as much as severalthousand feet. Moreover, the pressure which would be high enough tostart gas lift by such steady application, thatis,

a much lower pressure, this being made possible by the much lowerdensity of the gasand-oil column in the flow tube duringnormal lgas liftas compared with the oil before gaslift.- Thus, it is clear that it isnot convement or desirable to maintain said excessive pressure merelyfor the purpose of overcoming said hydrostatic head` The termhydrostatic head except where otherwise defined, is used throughoutthis.

case to mean the pressure of that portion of the oil body accumulated inthewell hole, which 'stands as a column inthe tube and Ycasing-above thelower end of the flow tube.

When a well has stood idle for a short time (a few hoursor a few daysaccording to the well), the head will have reached substantially itsmaximum height and will be in substantial equilibrium with the rockpressure in the vicinity -of the hole.v The term rock pressure is usedto signify the' natural expulsive pressure which forces the oil into thewell from the formation, and under the conditions just describedapproximately equals said hydrostatic head in the Well hole. Obviously,then, in a non-flowing Well under these conditions the said rockpressure or hydrostatic head -is less than the static head representedby the length of the flow tube between its points of intake anddischarge.

If gas under pressure be appliedl to the casing for example, of a .wellcontaining an accumulatedhead of oil, oil willv be forced up into thetube, thereby increasing the static head therein, as above indicated. Ofcourse, if the oil level stands sufficiently high in the well,1 theavailable gas pressure may elevate the oil in the tubing sulliciently todischarge some oil from the tubingwithout uncovering the lower endthereof, but discharge will cease as soon as the oil level becomesdepressed to such a point that the head in the pressure being applied.

In order to initiate gaslift by straight application of pressure, astarting pressure under the tubing, this pressure being here termed thenormal starting pressure. Such a pressure must be at leastequal,towthe.in-'- creased static head thereby developdin lthe' iowtube. This increased head of oil in the tubing is here termed the normal"starting head, the relative size of the tubing and casing, the amountand density and viscosity of the oil linl the well, the rock pressure,the friction of the formation, etc. The normalstarting head as the termis herein employed' is defined as the hydrostatic head of oil in theflow tubeabove the point of admission to said flow tube at the time gaswould 'break into the flow tube. In like manner, the normal startingpressure is defined as the gas pressure necessary to depress the oillevel in the gas -admission tube tol the pointv of gas admission totheflow tube and `suflicient to start gas lift in the liow tube when saidpressure is applied to the surface of the oil in said gas admissiontube. It is observed that the definition applies whether discharge iiowisfrom the tubeand gas application is through the casing, or vice-versa.If a lgas tube is employed and is connected by, a jet to the flow tubein a manner common to air or gas lift, the starting head or pressure maybe equal to the hydrostatic head -of the oil in the flow tube abovethe`jet when gas is irst forced into the gas tube, and it may be equalto or slightly greater than the hydrostatic head of oil above the jetwhenfirst applied.

The general object of the present invention,

is to overcome the hydrostatic head and de `press the oil levelapproximately to the lowf erend of the flow tube by the application ofgas under a pressure less than that required to initiate gas lift bysteady application to either the tube or' thecasing in the usual manner,and less than the hydrostatic head naturally existing in the well vpriorto gas lift initiation,

This object is attained 'hy promoting the absorption of a large amountof gas (natural gas preferred) by the oil body, coupled with adepression of the oil-level to as low a point as possible with theavailable pressure, whereby the absorbed gas materially reduces thespecific gravity of at least the upper portion i.

i of the' oil bodv and whereby the availble pressure then becomessuicientto elevate and disch-arge the column of the so-lightened oil inconjunction with the expansive and lifting properties ofthe. absorbedgas.

For convenience the present method is termed the rock-over method, sinceit comprises producing a series of impulses in one directionaltei-natedwith impulses inthe op-` posite direction-for the purposev ofalternatey raising' and lowerin each of the oil coll v l 'umns in thetubing an casing, the impulses must be employed sufficient tokdepressthe oilfg .level low enou h to allow the passage of gas.V

being timed and' applied tora'se the rising celumn higher'and higher'ineach instance forced out at the top,:this eiiect being assisted Lbygaswhich has been absorbed under the pressure produced. and by theagitation. re-

sulting from'the alternating or rocking ac- `tion'. and its magnitude isdependent upon such as 'airl but preferably a solublegas such asnaturalgas, under a` ressure which, if steadily applied, is insu cienttoovercome the normal starting head of the well`,this gas under pressurebeing applied first to one side of the tubing and then to the other,while the opposite side is released in each instance, so as to rock thetwo oil columns to and fro as above indicated and to agitate and mix theoil body in the casing and in the flow tube whereb appreciablequantities of gas are absorbed y the oil and serve to lighten the oilcolumns, this absorbed gas being capable .of expandingbin the upperportion of the column to be discharged so that such expansion evei 1tually will assist the operation sufiiciently to until the risingoilcolumnf is eventually i carry over at least a small proportion of theoil body, and repeating the alternate pressure applications as often asnecessary to estab lish flow.

Subject 'matter disclosed of the generic invention, is covered in mycopending and'206,6

In the accompanying drawings wherein oil mnlvements are representeddiagrammati- Ca y,

Fig. .1 indicates the oil level as it stands initially inthe casing andflow tube;

Fig. 2 indicates the iirst operation of a method which is usuallypracticed wherein gas under pressure is applied to the casing outsidethe flow tube;`

Abut not herein' claimed, together With various modificationsapplications, Serial Numbers 206,67 7

Fig. 3 indicates the second operation wherein the pressure applicationis yreversed time;

Fig. 4*-indicates a subsequent operation wherein the pressure is againapplied to the casing and the quantity of oil is v thereby pushed out'from the top ofthe liow tube.

Fig. 5 indicates the condition nally attained, that is, normal gas lift.f' l In these drawings there is shown a well casing 10 into which a flowtube 12 depends through the casing head, said casing head be.

ing also provided with a connection 14 throughwhich gas under pressuremay be introduced from compressor C. The level of.

the oil whichhas accumulatedin the tube and and yapplied to vthe iiowtube at the proper izo maaien the casing prior to institution of gaslift proceedings is indicated by line 15, it being the l function of thepresent invention to reduce this static head by forcing said oil leveldown to the lower end of the flow tube kl2 whereby gas `will flowundersaid tube to atomize the oil and thereby initiate normal gas lift.,

Ordinarily, the operation is started by iirst p applying the gas underpressure to the surface of the oil in the casing, said gas beingintroduced through the connection 14 and the flow tube 12 being leftopen at its upper. end. The pressure is built up in'the casing to theavail# able maximum to cause the oil level to rise in the tube as highas possible and until the static head of oil in the tube equalizes saidpressure, the depressed oil level in the casing being indicated at 16,and the level attained in the tube being indicated at 18 in Fig. 2.

0 Under these conditions some oil-may be forced.

` back into the formation, thus further lower- 'ing the oil level. Thepressure in the casing is then released and the gas under pressure istransferred to the flow tube by way of con- `nection 19 to follow up thegravity descent of the oil column so as to take advantage of themomentum of such descending column;

Under thispressure application the oil level in the casing is elevatedto as high a point as possible, by depression of the level in the tubeto as loW a point as possible. In Fig. 3

the dotted line 2O represents the probable limit of descentl of the oilcolumn in tube 12 which would occur by gravity and momentum alone andthe dotted line 22 represents the corresponding elevation in the casing,While the line 24 represents the depression of the oil in the column 12underthe application of pressure, andthe line 25 indicates thecorresponding elevation in the casing. These points having been reachedthe tube pressure is released and gas under pressure is again applied tothe casing, the momentum of the moving oil again being relied upon toassist depressing theoil column as far as possible. Thisalternate'application of gas under pres sure on one side with releasedpressure on the other side, is repeated as often as necessary and theoil columns are thereby caused to surge back and forth in conjunctionwith the influences of gravity and momentum whereby an appreciableamount of agitation is produced and contact of the oil with the gas isincreased with a resultant increase in gas absorption, which absorption,of course, is materially assisted by the pressure under which the gas isintroduced. The gravity descent of the oil column in the casing, whicheventually-perhaps would reach point 26 with Y o0 a correspondingelevation in the tube to the point 27, taken in conjunction with theapplication of pressure to thecasing` through the connection 14 willcause an eventual depression of the oil level in the casing to the point28 as indicated in Fig. 4 with a consequent if the headwere sucientlylow.

All of the alternate pressure applications y are properly timed atintervals to correspond with the beginning of descent of'the respectiveoil columns,I this timing beingdetermined by Watching the pressuregauges; the result is that said columns are caused not only to surgeback and forth but also to rise higher and higher on the respectivesides until a quantity of the oil is sent over. It is important thatthis rocking or surging motion so timed as to obtam the lmaximum surgewith the greatestl possible rapidity, since such timing vresults intaking the greatest advantage of the .momentum of the moving oilcolumns. In this fashion the combined influence of such momentum 'of theoil bodies, together with the pressure under which the gas isintroduced` and the expansive influences of the absorbed gas, eventuallyresult in establishing continuous flow from the Well, by depression ofthe oil level-to approximately the lower end of the iow tube 12 asindicated in Fig. 5, so that the gas will iiow around the lower end ofsaid tube, thereby atomizing the adjacent oil and carryingzit upwardthrough the tube in amounts corresponding to the natural oil flow intothe well. rdinarily, How may then be continued with a lower pressurethan Was required for starting.

Usually it is not possible to cause flow of any great amount of oil overthe top in the beginning, since the'head of the relatively heavy oil inthe flow'tube above the level in the casing will become too great to beovercome by the gas pressure. But at each sue-r cessive impulse anadditional small amount of oil ordinarily will be expelled and at eachoperation additional amounts of gas will be absorbed until the oil bodyis isuiicientlyrely'norm'al How, if desired, mayv be 'established fromthe casing rather than from the tubing and it is to be understood thatthe invention is the same regardless of the direction of the flowfinally established, especially since the initiating steps will be thesame.

The method above outlined may be varied by keeping the flow tube closedfor a time when the casing is placed under pressure, in order toincrease gas absorption. Sometimes when the hydrostatic head is low andonly a slight amount. of absorption and agitation is required to startgas lift, the Well will commence to How upon sudden release of vthiscient to continue gas lift.

It is to beunderstpod that the above/disv; closures are merelyillustrative, and that many variations of the inventionl maybe madeWithin the scope of the following clalms as will be apparent to-thoseslzilled in the art.

I claim:

l. In a method for initiating gas lift infan oil well containing acasing and a body of oil into which a flow tube depends, thesteps'comprising introducing gas under pressure into. the casing on oneside ofthe tube to elevate a column of oil on the other side of thetube, re-

leasing the pressure and allowing the elevated oil column to return tobe mixed with said l body of oil. f

2.' In a method for initiating gas lift in an oil well containing-acasing into which a-flow tube depends, the steps'comprising introducinggasunder pressure into the casing' to an- Y proximate the maximumpressure attainable with the available pressure whereby the oil f bodybecomes charged with a gas, releasing p ing introducing gas underpressure into the the pressure in the casing, and-repeating theseoperations until the oil becomes charged with gas suicient to insuredischarge of a portion of the oil` v3. In a method for initiating gaslift operation in an oil well containing a casing into which a flow tubedepends, the steps compriscasing whereby an oil column is elevated inthe tube and the oil body becomes charged with gas, releasing thepressure in the. casing and allowin -t-he oil column to'return, re-

,peatin this operation until the oil becomes charge withgas 'suilicientto insure discharge ofl a portion of the oil, then placing the, casingagain under pressure and venting the flow tube to discharge a portion ofVthe charged oil.

4. In a method for initiating gas lift operation in an. oil well havinga casing containing abody of oil into which `a ilow tube depends. thesteps comprising introducing gas into the casing under pressure lessthan, the,

normal starting pressure wherebysaid pressure-elevates the oil column inthe tube, re-

' leasing the pressure in the casing land allowing the oil column toreturn, repeating this operation until the oil becomescharged with i gassufficient to insure discharge of a portion j of the oil, then placingthe casing a ain under pressure and ventingthe flow tu e to dis- -chargea portion of the charged oil, and re- Y iframes peating this operationto force out` successive portions of theoil until the level 1n the wellis lowered suiiiciently to establish normal gas lift operation.

5. In a method for initiating gas lift operations in an oil wellcontaining a casing in ,which theflow tube depends, the steps comprisingintroducing gas under pressure into the casing to approximately themaximum pressure attainable with'the available pressure and forelevation vof an oil column in. the tube, releasing the pressure in thecasin to allow said oil column to descend 'an' simultaneously applyingthe available gas pressure to the descending'columnuntil said descendingcolumn has been depressed as faras possible, releasing the pressure in'the tube to allow the oil column in the casing to descend, and repeatingthese operations until y normal gas lift is established.

' 6. In a method for initiating gas lift operations in an oil wellcontaining a casing into which a ow tube depends, the steps ofintroducing gas into the lcasing under pressure less than that normallyrequired to force gas under the lower end ot the flow tube, to depressthe oil body in the casing as far as possible and to .elevate anoil-column in the tube as far-as possible with said pressure, releasingthel pressure in the casing to allow the oil column in the Vtube todescend and Simultaneously applyingpressure to the tube to depress thecolumn therein as far as possible, releasing the'pressure in the tubeand repeitfing the above steps to establish normal gas 1 t.

" 7. In a method for initiating gas-lift operations in an oil well, thesteps comprising bringing gas under pressure into contact with thesurface of an oil body in a well, and agitatino the oil to charge thesame with gas.

8. In a method for initiating gas lift oper- -ations in an oil well, thesteps comprising bringing a` soluble gas under pressure-into contactwith the surface of an oil body in a well, and afgitating the oil byliuctuating the level thereof to charge the oil with the gas. f9. In amethod for initiating gas lift in oil wells, the steps comprisingbringing -'gas under pressure into contact' with fil in a wellV intowhich a tube depends and by variation in gas pressures upon 'theopposite sides of the tube causing the oilbody to rock to and frowhereby' the oil is mixed with and becomes charged with gas.`

10. In a method for initiating gas lift in an oil well containing acasing and a body of accumulated oil into which a flow tube depends,thesteps comprising alternately applying series of impulses on oppositesides of the flow tube to alternately raise and lower the oil columns inthe tube and casing. .11. In a methodsfor initiating gas lift in an oilwell containing a casing and a body of accumulated oil into which a flowtube de-

